Question about differences between Cobra and Lightning stock boost maker

[thomas91169]

So my buddy just got a 2g Lightning and was commenting on pulley sizes, said stock upper was 2.93". I was taken by surprise and called bs seeing stock 03/04 Cobra upper is what, 3.65"? he proved me wrong. Then figured it was a difference in the lowers, but both have a ~7.5" lower.

What gives? What am I missing in the equation?

Both vehicles make 8psi stock.
Both vehicles have a 7.5" lower
Both vehicles have the same Eaton M112 blower.

Am I retarded? Or just bored and seeking knowledges.

 

[Ironhand]

M112 on 03 DOHC 4.6 vs. M112 on Lightning 5.4 2 Valve. Its the displacement!

Stock Cobra size is 3.65 and Lightning is indeed 2.93. Some of the first Cobra mods were to actually put a lightning 2.93 upper on the 03s way back in the day.

 

[meaty mac]

^^^^^^^^^^^
Yup. Also why L's go to a Lower pulley for more boost, right off the bat.

 

[thomas91169]

M112 on 03 DOHC 4.6 vs. M112 on Lightning 5.4 2 Valve. Its the displacement!

Stock Cobra size is 3.65 and Lightning is indeed 2.93. Some of the first Cobra mods were to actually put a lightning 2.93 upper on the 03s way back in the day.

"boost" or PSI is a measure of restriction, right?. If both vehicles are making around 8psi stock, yet the blower on the 5.4 2v is spinning faster than the one on the 4.6 4v, wouldnt that mean that the 5.4 2v is the more restrictive of the two :shrug:

but I guess if the 5.4 does "consume" more of that air due to being able to engulf more on the intake stroke due to displacement, then that would also account for the difference, but damn, I didnt think it would be that much.

knowledge ftw.

 

[99riocobra]

^ Your second statement is more the correct way of thinking of this. The eaton M112 displaces 112ci(1.835L) of air per revolution. The larger volume of displacement in the lightning vs the cobra means that each cylinder takes a larger volume of air to fill it, due to a longer stroke in the 5.4 in this case. Since it takes more air to fill the cylinders the supercharger needs to "send" more air compared to the smaller 4.6 to create the same amount of back pressure(boost). This is achieved by spinning the blower harder via the smaller pulley, the supercharger will displace more air per revolution of the crank in this case.